The SEC subpoenaed Bank of America, Citi, JPMorgan, Goldman Sachs and Wells Fargo last week over their processes during the early stages of securitizing home loans, Reuters reported.

The SEC wants to know more about so-called "master servicers" - firms that specialize in administering the selection and maintenance of the huge pool of home loans that are packaged together for every mortgage-backed bond.

This is the second phase of the SEC's probe into mortgage-related activities at each of the banks.

"Now the SEC is looking at how the lenders packaged up mortgages for sale to investors," tipsters told Reuters.

[T]he SEC is seeking information about the role banks had in mortgage securitization. The regulator is also looking at the role trustees for the trusts that issued the mortgage-backed securities had in monitoring the performance of the underlying loans. The SEC is looking at whether loans were properly transferred to the trusts that issued the securities.

None of the banks confirmed having received an SEC request for documents.